/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.core;



import com.bff.gaia.unified.sdk.state.ReadableState;

import com.bff.gaia.unified.sdk.state.Timers;

import com.bff.gaia.unified.sdk.transforms.windowing.BoundedWindow;

import com.bff.gaia.unified.sdk.transforms.windowing.PaneInfo;

import com.bff.gaia.unified.sdk.values.WindowingStrategy;

import org.joda.time.Instant;



import java.io.Serializable;



/**

 * Specification for processing to happen after elements have been grouped by key.

 *

 * @param <K> The type of key being processed.

 * @param <InputT> The type of input values associated with the key.

 * @param <OutputT> The output type that will be produced for each key.

 * @param <W> The type of windows this operates on.

 */

public abstract class ReduceFn<K, InputT, OutputT, W extends BoundedWindow>

    implements Serializable {



  /** Information accessible to all the processing methods in this {@code ReduceFn}. */

  public abstract class Context {

    /** Return the key that is being processed. */

    public abstract K key();



    /** The window that is being processed. */

    public abstract W window();



    /** Access the current {@link WindowingStrategy}. */

    public abstract WindowingStrategy<?, W> windowingStrategy();



    /** Return the interface for accessing state. */

    public abstract StateAccessor<K> state();



    /** Return the interface for accessing timers. */

    public abstract Timers timers();

  }



  /** Information accessible within {@link #processValue}. */

  public abstract class ProcessValueContext extends Context {

    /** Return the actual value being processed. */

    public abstract InputT value();



    /** Return the timestamp associated with the value. */

    public abstract Instant timestamp();

  }



  /** Information accessible within {@link #onMerge}. */

  public abstract class OnMergeContext extends Context {

    /** Return the interface for accessing state. */

    @Override

    public abstract MergingStateAccessor<K, W> state();

  }



  /** Information accessible within {@link #onTrigger}. */

  public abstract class OnTriggerContext extends Context {

    /** Returns the {@link PaneInfo} for the trigger firing being processed. */

    public abstract PaneInfo paneInfo();



    /** Output the given value in the current window. */

    public abstract void output(OutputT value);

  }



  //////////////////////////////////////////////////////////////////////////////////////////////////



  /** Called for each value of type {@code InputT} associated with the current key. */

  public abstract void processValue(ProcessValueContext c) throws Exception;



  /** Called when windows are merged. */

  public abstract void onMerge(OnMergeContext context) throws Exception;



  /**

   * Called when triggers fire.

   *

   * <p>Implementations of {@link ReduceFn} should call {@link OnTriggerContext#output} to emit any

   * results that should be included in the pane produced by this trigger firing.

   */

  public abstract void onTrigger(OnTriggerContext context) throws Exception;



  /**

   * Called before {@link #onMerge} is invoked to provide an opportunity to prefetch any needed

   * state.

   *

   * @param c Context to use prefetch from.

   */

  public void prefetchOnMerge(MergingStateAccessor<K, W> c) throws Exception {}



  /**

   * Called before {@link #onTrigger} is invoked to provide an opportunity to prefetch any needed

   * state.

   *

   * @param context Context to use prefetch from.

   */

  public void prefetchOnTrigger(StateAccessor<K> context) {}



  /**

   * Called to clear any persisted state that the {@link ReduceFn} may be holding. This will be

   * called when the windowing is closing and will receive no future interactions.

   */

  public abstract void clearState(Context context) throws Exception;



  /** Returns true if the there is no buffered state. */

  public abstract ReadableState<Boolean> isEmpty(StateAccessor<K> context);

}